porous materials made from hard rubbers and latexes.
The manufacture of porous rubbers from hard rubbers involves the use of compounds containing blowing agents in addition to such standard ingredients as fillers, plasticizers, and vulcanizing systems. The blowing agents decompose at temperatures near the vulcanization point to yield gaseous products. Closed-celled cellular rubbers are obtained with the aid of organic blowing agents and high-pressure vulcanization, with pressures sometimes reaching 20-30 meganewtons/m2 (200–300 kilograms-force/cm2). These materials are also called “expanded rubbers.” The use of such inorganic blowing agents as sodium bicarbonate together with vulcanization at normal pressure results in the formation of cellular rubbers with predominantly connecting pores. Blowing agents are not used in the manufacture of latex foam rubber. The cellular structure (up to 95 percent connecting pores out of the total porosity) is formed by mechanically frothing the latex mixture and by gelling and vulcanizing the resulting foam.
The pore size in cellular rubbers may vary from ~0.4μ in microporous rubbers to 0.2-0.4 mm in foam rubber. Cellular rubbers have low density (0.06-0.80 g/cm3), high compressive strength (particularly, expanded rubbers), and soundproofing and heat-insulating properties; the coefficient of thermal conductivity is 0.039-0.044 W/(m-°K), or 0.035-0.038 kcal/(m·hr. °C). Cellular rubbers also inhibit vibration. They are used in the manufacture of such products as packing materials, automobile and airplane seat cushions, mattresses, insulating layers for synthetic floor coverings, and shoe soles.